Conventionally known bioactive ceramics capable of chemically bonding to bone include sintered apatite and Na.sub.2 O--K.sub.2 O--MaO--CaO--SiO.sub.2 --P.sub.2 O.sub.5 glass ceramic, as described in M. Akao et al, J. Mater. Sci., 16, 809 (1981), G. DeWith et al, J. Mater. Sci., 16, 1592 (1981), B. A. Blencke et al, Med. Orthop. Tech., 95, 144 (1975), V. Strunz et al, Dtsch. Zahnarztl. Z., 32, 287 (1977), and H. Bromer et al, Science of Ceramics, 9, 219 (1977). Further, glass ceramics containing apatite crystals and wollastonite crystals are also known, which is produced by grinding MgO--CaO--P.sub.2 O.sub.5 --SiO.sub.2 type glass to 75 .mu.m or smaller, molding the glass powder, heat-treating the glass powder at a sintering temperature and then at a temperature for forming an apatite crystal [Ca.sub.10 (PO.sub.4).sub.6 (O.sub.0.5,F).sub.2 ] and a wollastonite crystal [CaSiO.sub.3 ], as described in Japanese Patent Application (OPI) No. 191252/82, T. Kokubo et al, J. Mater. Sci., 20, 2001 (1985) and T. Kokubo et al, Chikkyo, 90, 151 (1982). In this glass ceramic, the apatite crystal contributes to biocompatibility and the wollastonite crystal contributes to mechanical strength. Hence, it is desirable to increase the wollastonite crystal content in order to enhance mechanical strength properties.
Bending strength of the sintered apatite is from 1,000 to 1,400 kg/cm.sup.2 ; that of Na.sub.2 O--K.sub.2 O--MgO--CaO--SiO.sub.2 --P.sub.2 O.sub.5 glass ceramic is from 1,000 to 1,500 kg/cm.sup.2 ; and that of MgO--CaO--P.sub.2 O.sub.5 --SiO.sub.2 type glass ceramic is from 1,200 to 1,400 kg/cm.sup.2. However, this bending strength level is still unsatisfactory as artificial dental roots or artifical bone.